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[0806.4493] Statistical and systematical errors in cosmic microwave background maps
 
Authors:Hao Liu, Ti-Pei Li
Abstract:Sky temperature map of the cosmic microwave background (CMB) is one of the premier probes of cosmology. To minimize instrumentally induced systematic errors, CMB anisotropy experiments measure temperature differences across the sky using paires of horn antennas with a fixed separation angle, temperature maps are recovered from temperature differences obtained in sky survey through a map-making procedure. The instrument noise, inhomogeneities of the sky coverage and sky temperature inevitably produce statistical and systematical errors in recovered temperature maps. We show in this paper that observation-dependent noise and systematic temperature distortion contained in released Wilkinson Microwave Anisotropy Probe (WMAP) CMB maps are remarkable. These errors can contribute to large-scale anomalies detected in WMAP maps and distort the angular power spectrum as well. It is needed to remake temperature maps from original WMAP differential data with modified map-making procedure to avoid observation-dependent noise and systematic distortion in recovered maps.
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Thomas Dent



Joined: 14 Nov 2006
Posts: 28
Affiliation: ITP Heidelberg
PostPosted: June 30 2008  Reply with quote
Since I am not a CMB analyst I will simply call for comments on this.

I got as far as understanding Fig.1 which shows the WMAP3 sky coverage in terms of the number of observations N per pixel, the 1/sqrt(N) expected noise - and the large-scale anomalies up to l=2. The results being curiously similar.

The argument seems to be that the large-scale anomalies are suspiciously aligned with the WMAP sky coverage and there is a direct link due to 'exposure-dependent noise'.

They claim another effect of 'systematic temperature distortion' due to the differencing procedure, which produces spurious 'rings' of anomalously cold pixels around hot point sources.

Too bad they did not get to WMAP5...
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